X-raying stellar winds in a high-speed collision

October 12, 2012

XMM-Newton observation of the core of the very massive cluster Cyg OB2 located in the constellation of Cygnus, 4700 light-years from Earth. The cluster contains massive O-type stars that shine brightly in X-rays. Cyg OB2 #9 is seen as the bright star just below the central star, and in 2008 was determined to be a binary system. ESA’s XMM-Newton and NASA’s Swift space telescopes have now found evidence for the winds of these hot, massive stars colliding at the closest points of their orbits, resulting in a four-fold increase in X-ray emission. Hundreds of lower mass stars also fill the field of view, which spans nearly 22 x 16 arcminutes. Credits: ESA/G. Rauw

(Phys.org)—Two massive stars racing in orbit around each other have had their colliding stellar winds X-rayed for the first time, thanks to the combined efforts of ESA's XMM-Newton and NASA's Swift space telescopes.

Stellar winds, pushed away from a massive star's surface by its intense light, can have a profound influence on their environment.

In some locations, they may trigger the collapse of surrounding clouds of gas and dust to form new stars.

In others, they may blast the clouds away before they have the chance to get started.

This is an artist's rendering of a colliding wind binary. Credit: NASA/C. Reed

Now, XMM-Newton and Swift have found a 'Rosetta stone' for such winds in a binary system known as Cyg OB2 #9, located in the Cygnus star-forming region, where the winds from two massive stars orbiting around each other collide at high speeds.

This video is not supported by your browser at this time.

This computer simulation shows the gas density around a colliding wind binary named WR 22. The star locations are marked by yellow dots, and decreasing gas density is indicated by the sequence of red, white and blue colours. In this simulation, a 26-solar-mass O-type star orbits the hotter and more massive (72 solar mass) Wolf-Rayet star WR 22. Because WR 22 possesses the stronger stellar wind, a bow shock and wake is formed by the O star as it orbits. The stellar orbits are eccentric, so the separation contracts and expands. Consequently, the conditions in the shocked gas around the O star changes; as the stars near closest approach, the gas cools so effectively that it becomes very clumpy. During closest approach, WR 22's stellar wind is so intense that the region where the winds collide is actually forced back onto the O star. Such a collapse of the wind region does not occur with Cygnus OB2 #9, which makes it a well-behaved system for exploring wind-wind interactions. Simulations like this are being applied to Cygnus OB2 #9 in support of the recent observational campaign to help unravel the properties of its wind-wind collision. Copyright: Australian National University/E.R. Parkin, University of Liège/E. Gosset

Cyg OB2 #9 remained a puzzle for many years. Its peculiar radio emission could only be explained if the object was not a single star but two, a hypothesis that was confirmed in 2008.

At the time of the discovery, however, there was no direct evidence for the winds from the two stars colliding, even though the X-ray signature of such a phenomenon was expected.

This video is not supported by your browser at this time.

The Cygnus OB2 #9 binary system consists of two nearly equal-mass O stars that follow an eccentric orbit around their common centre of gravity. Observations with ESA's XMM-Newton and NASA's Swift observatories showed a quadrupling of X-ray flux around the time of periastron (June/July 2011) - when the stars were close together in their orbits. This has provided the first concrete evidence that a wind-wind collision is taking place in this system. Previous observations with XMM-Newton had hinted at the presence of colliding stellar winds but those observations were carried out when the two stars were far from each other. Copyright: NASA/Goddard Space Flight Center

This signature could only be found by tracking the stars as they neared the closest point on their 2.4-year orbit around each other, an opportunity that presented itself between June and July 2011.

As the space telescopes looked on, the fierce stellar winds slammed together at speeds of several million kilometres per hour, generating hot plasma at a million degrees which then shone brightly in X-rays.

The telescopes recorded a four-fold increase in energy compared with the normal X-ray emission seen when the stars were further apart on their elliptical orbit.

"This is the first time that we have found clear evidence for colliding winds in this system," says Yael Nazé of the Université de Liège, Belgium, and lead author of the paper describing the results reported in Astronomy & Astrophysics.

"We only have a few other examples of winds in binary systems crashing together, but this one example can really be considered an archetype for this phenomenon."

This video is not supported by your browser at this time.

O-type stars are among the most massive and hottest known, pounding their surroundings with intense ultraviolet light and powerful outflows called stellar winds. NASA's Swift and ESA's XMM-Newton X-ray observatories took part in a 2011 campaign to monitor the interaction of two O stars bound together in the same binary system: Cygnus OB2 #9. Credit: NASA's Goddard Space Flight Center

Unlike the handful of other colliding wind systems, the style of the collision in Cyg OB2 #9 remains the same throughout the stars' orbit, despite the increase in intensity as the two winds meet.

"In other examples the collision is turbulent; the winds of one star might crash onto the other when they are at their closest, causing a sudden drop in X-ray emission," says Dr Nazé.

"But in the Cyg OB2 #9 system there is no such observation, so we can consider it the first 'simple' example that has been discovered – that really is the key to developing better models to help understand the characteristics of these powerful stellar winds. "

"This particular binary system represents an important stepping stone in our understanding of stellar wind collisions and their associated emissions, and could only be achieved by tracking the two stars orbiting around each other with X-ray telescopes," adds ESA's XMM-Newton project scientist Norbert Schartel.

Related Stories

Today the Chandra X-ray Observatory released an image from a research group led by Leisa Townsley of the Penn State Department of Astronomy and Astrophysics. The image of the star cluster Trumpler 14 shows about 1,600 stars ...

NASA's Chandra X-ray Observatory is helping to demystify Westerlund 2, a young star cluster with an estimated age of about one- or two-million years. Heavily obscured by dust and gas, Westerlund 2 has been something of a ...

Many types of main sequence stars emit in the X-ray portion of the spectra. In massive stars, strong stellar winds ripping through the extended atmosphere of the star create X-ray photons. On lower mass stars, magnetic fields ...

(PhysOrg.com) -- The Great Nebula in the constellation of Carina is a massive star-forming complex located about 7.5 thousand light-years away. The main star in the complex, Eta Carinae, shines brightly in the southern sky. ...

(PhysOrg.com) -- The Sun, glowing with a surface temperature of about 5500 degrees Celsius, warms the Earth with its salutary light. Meanwhile the Sun's hot outer layer (the corona), with its temperature of over a million ...

The well known Orion Nebula is perhaps the most well known star forming regions in the sky. The four massive stars known as the trapezium illuminate the massive cloud of gas and dust busily forming into new stars providing ...

Recommended for you

What if I told you that recent experiments have revealed a revolutionary new method of propulsion that threatens to overthrow the laws of physics as we know them? That its inventor claims it could allow us to travel to the ...

The coalescence of two black holes—a very violent and exotic event—is one of the most sought-after observations of modern astronomy. But, as these mergers emit no light of any kind, finding such elusive events has been ...

The recent discovery of an Earth twin has boosted chances there is intelligent life on other planets. But while Pope Francis's telescope scans the starlit skies, the Vatican is sceptical of ever meeting Mr. Spock.

A dying star's final moments are captured in this image from the NASA/ESA Hubble Space Telescope. The death throes of this star may only last mere moments on a cosmological timescale, but this star's demise is still quite ...

3 comments

The behavior of plasma cannot be described with mechanical interactions, such as winds "slamming" into each other, plasma behaves electrodynamically. That being said, the validity of this paper must be in question.

Re: "This is the first time that we have found clear evidence for colliding winds in this system"

When we slam charged particles together in colliders, we do not call this a collision of "winds." The wind metaphor is misleading insofar as it induces people to equate the behavior of quasi-neutral cosmic plasmas with that of neutral gases. Considering that astrophysicists still can't identify the actual accelerating source of these "winds," we'd be wise to recall that in the laboratory, the easiest way to accelerate a charged particle is to subject it to an electric field. But, this presents conventional theorists with a predicament: If the Sun is the center of an electric field, then what replenishes the charge after that charge disperses, due to the field? The E-field inference is in this way a dead-end for many theorists for the very reason that it is suggestive of an ELECTRODYNAMIC universe. They simply refuse to ask the questions which might validate that different worldview.

The behavior of plasma cannot be described with mechanical interactions, such as winds "slamming" into each other, plasma behaves electrodynamically. That being said, the validity of this paper must be in question.

When I saw the title of the article and two comments, I checked on what the Schrodinger equations would predict. His math is still spot on,,,, 99.99999% that one of the two comments would would have plasma 1/2 spin up.

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.